Weapons such as rifles and the like that employ a stock are meant to be used by pressing the stock into the shoulder area of the shooter. Such use and placement allows the shooter to have greater control over the motion (or stillness) of the weapon when aiming so that the weapon may be fired more accurately. Typically, proper placement of a weapon is such that over 90% of the surface area of the butt stock of the weapon is in contact with the shoulder of the shooter.
A problem arises when shooters are using body armor such as Kevlar vests and the like. The body armor changes the silhouette of the shooter's shoulder in such a way as to prevent effective positioning of the butt stock of the weapon. In many cases, the shooter is using less than 50% of the surface area of the butt stock when aiming and firing the weapon. This leads to aiming problems and can be the difference between life and death for the shooter in a combat situation.